Emergency repairs began Tuesday at 8:00 p.m. on I-75 South at the site of Monday's beam collapse. 

Engineers with the Tennessee Department of Transportation believe an over-sized load hit the bottom of the bridge as it drove under on I-24, causing the collapse.

TDOT's Chief Engineer, Paul Deggers said Tuesday during a press conference over-sized loads hitting bridges isn't unheard of, saying it happens in Tennessee about 50 times a year. 

Drivers are supposed to report incidents when they happen, but Deggers said that doesn't always happen. 

Deggers said there were no incidents reported to TDOT about the bridge that collapsed Monday, but said forensic evidence on the bridge and the beam that collapsed led them to believe an over-sized load hit it. 

TDOT is working with Tennessee Highway Patrol to try and find the company responsible by looking at video and weigh station logs in the days prior to the incident.

In the meantime, crews are working on an emergency fix to replace the beam. 

"[We will install a] barrier rail up on the bridge so we can get two lanes of traffic. It'll probably be a little bit narrower than it is today or before the beam fell but it'll still allow us to get two full lanes," he said. 

The emergency repair will take about two weeks to complete, weather permitting and will be paid for through TDOT's bridge repair fund. 

A 2017 report shows of the 500 bridges in Hamilton County, about 25% have a sufficiency rating at or below the one involved in the partial collapse. 

The I-75 S bridge at the I-24 interchange had a rating of 74.7 on a 100 point scale. 

The Market Street bridge had a sufficiency rating of 31.5 and the Highway 58 ramps at Highway 153 had a rating of 33. 

Deggers said sufficiency ratings do not correlate with safety, saying if a bridge is open, it is safe. 

"Most of the issues with bridges are in the riding surface, the bridge deck. But they all have steel under there. Even if the concrete fell out, it'd be a rough ride, but you could ride over the steel and the bridge wouldn't collapse," he said. "If a bridge is open to traffic, it's safe. If a bridge is not safe, we're going to close it. If it's on our network, we'll close it. If it's owned by a local government or other entity, we'll tell them to close it."

If there are signs posted with weight or height restrictions, Deggers said it's important for drivers to abide by those.

The following is a time frame from TDOT for the repair work to the I-75 South bridge: 

Work to restore the I-75 South bridge to two lanes will begin Tuesday at 8:00 p.m. and last until 6:00 a.m. the following morning. The contractor will stop working during morning rush hours from 6:00 a.m. to 10:00 a.m., and continue to working seven days a week until the work is completed. 

During the repair work to the I-75 South bridge, the ramp to I-24 West beneath the bridge will be reduced to one lane. This work is expected to take about two weeks to finish depending on the weather conditions.

Drivers who travel through this area are urged to be patient and to watch for workers and equipment.

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